1. Field of the Invention
This invention pertains to the bonding together of high performance parts, one of which is rubber or other elastomer and the other part being plastic or metal and more particularly to the bonding together of such parts that are part of a well head blowout preventer.
2. Description of the Prior Art
There are chemical bonding materials that are considered to be high performing in applications where an elastomer, typically rubber, is bonded or adhered to a dissimilar material, such as plastic or metal. One such application is in blowout preventers where the packer for closing off the annulus of a well, sometimes under emergency conditions, is made up of a combination of elastomer and plastic and/or metal parts. Typically, the packer either closes around a well pipe extending through the central bore or opening of the blowout preventer, or packer assemblies close together after the well pipe is sheared off.
The bonding of parts is necessary to prevent the elastomer parts from separating from the dissimilar material parts when subjected to extremely high pressures (e.g., 10,000 to 20,000 psi) or extremely high pressures and temperatures (e.g., 180.degree. F. to 400.degree. F.). A slight separation becomes a problem in the overall operation in two main ways. First, a slightly separated part changes the dimensioning of the assembly of parts, which dimensional change can interfere with normal operation and can cause the interfering part to be cut off when operation forces the closing or opening of other parts of the assembly. Thus, a separated elastomer part that is supposed to seal is often cut off so that it no longer adequately seals in the intended manner. Secondly, separation of assembly parts, one of which is an elastomer that readily "flows" when subjected to extremely high pressures or high pressure and high temperatures, creates "gaps" and permits the extrusion of the elastomer between adjacent metal pieces where the metal-to-metal contact or fit is less than perfect. High pressures tend to extrude the elastomer through small gaps. High temperatures cause the elastomer to become soft, so when present together, elastomers extrude rather easily. Extrusion of the elastomer can result in both high pressure and low pressure leaks and other harmful conditions, which, if bad enough can result in premature wear-out of parts and even in creating dangerous operating conditions.
Even the toughest metal/plastic-to-elastomer bonding materials can fail under adverse conditions. First, the bonding material between metal or plastic and an elastomer is usually the weakest structural link of the assembly. Second, the composition material itself can degrade and either become soft or brittle. If it becomes soft, then the bonding material can itself extrude away from the bonding surface under high pressure conditions. If the material cracks, then it no longer is an acceptable bonding material. Third, however, and perhaps more importantly since bonding materials are known that exhibit reasonably stable properties even under extremely high pressures and temperatures, the interface surfaces of rubber and metal or rubber and plastic do not exhibit the same dimensional stability as each other under high pressure and high temperature conditions. That is, one surface will expand more than the other, thereby causing breakaway from the bonding material, especially after repeatedly being subjected to normal and then high pressure and high temperature conditions.
Thus, it is a feature of the present invention to provide an improved bonding of rubber or other elastomer to metal or plastic, which bonding must be maintained under extremely high pressure or high pressure and high temperature conditions.
It is another feature of the present invention to provide such an improved bonding in the parts of a blowout preventer.
It is still another feature of the present invention to provide such an improved bonding of parts in a blowout preventer by achieving a combination of a mechanical and a chemical bond.